1. Field of the Invention
This invention relates to a recording current setting method and an information signal recording apparatus to control VTR recording current to an optimal value.
2. Description of the Prior Art
According to the prior art, the control to set the recording current of VTR video signals has been so far made as mentioned below. First, signals are recorded on a tape for a preset period, 20 seconds for example, at a certain level of recording current. Then, the tape is rewound to a portion where the signals are recorded. The portion where the signals have been recorded are reproduced, and the level of the reproduced signals is measured at this recording current. Hereafter, the same process is repeated, while changing the recording current. Thus, a relation between recording current and reproduced signal level is determined. From the relation between recording current and reproduced signal level, an optimal level of recording current is obtained.
According to this method, however, time to record signals on a tape and time to rewind the tape are required, so that it takes a long time to obtain an optimal level of recording current.
To overcome this problem, it is proposed to set to an optimal level of recording current by repeating recording and reproduction with a tape remaining stopped.
In other words, the signals are recorded on the tape at a certain level of recording current, by setting the VTR to the recording mode with the tape stopped. Then, by setting the VTR to the reproduction mode, an RF envelope level of the reproduced signals is measured at that recording current. Thereafter, this process is repeated while changing the recording current. Thus, the relation between recording current and reproduced signal level is determined. From the relation between recording current and reproduced signal level, an optimum level of recording current is obtained.
Accordingly, since a relation between recording current and reproduced signal level is obtained by repeating recording and reproduction with the tape remaining stopped, time is not required to rewind a tape, which shortens a time period for setting the recording current.
The optimal setting value for recording current is a recording current where the reproduced signal level thus obtained arrives at its peak in a curve indicating the relation of the reproduced signal level with the recording current. The relation between envelope level of reproduced signals and recording current of video signals can be expressed approximately in a quadratic curve when graphing the change in the recording current logarithmically. According to the measurement data of the video signal recording current and reproduced RF signal envelope level, for example, it is possible to have an approximate expression for the quadratic curve by using the method of least squares, to calculate coordinates which are a vertex of the quadratic curve, and then to set an optimal recording current.
However, the process to seek an approximate expression is complicated, which requires a large program and much time. In particular, when the process is made by an 8-bit microcomputer, there will be an increase in rounding error and a decrease in accuracy.